@VallabhGopal

Technically it will probably work. The rules created in 8.x have more meta data within them, so saving them afterwards might not be possible though. Also missing referencing rules are a problem you would need to fix manually.

And for your application... It's most likely to break, as the activities, data transforms, etc your application depends on are different for both versions. For example, when rules might not be present in pega 7.x and you'll get a RuleNotFoundException at runtime. And contrary to your own created rules, pega ootb rules cannot be updated by you.

TLDR; don't do it!